1. Field of the Invention
The present invention relates to a honeycomb structural body made of cordierite, which is used as a catalyst carrier in an exhaust gas purification apparatus for an internal combustion engine.
2. Description of the Related Art
Catalyst carriers for exhaust gas purification apparatuses have conventionally employed a honeycomb structural body 9 such as shown in FIGS. 15A and 15B, wherein partition walls 90 made of cordierite or the like are arranged in a honeycomb fashion to form multiple cells 99. An exhaust gas purification function is exhibited by carrying an exhaust gas purifying catalyst on the surface of the partition walls 90 of the honeycomb structural body 9.
However, with the enforcement of stricter exhaust gas standards for automobiles in recent years, it has become necessary to achieve more rapid activation of the catalysts in exhaust gas purification apparatuses. Specifically, research has been carried out on lowering heat capacity and pressure loss by reducing the thickness of the partition walls in honeycomb structural bodies. Other studies have focused on moving the position where the catalyst carrier is mounted to be closer to the engine than usual to provide a higher-than-conventional temperature of the exhaust gas to be purified.
These conventional honeycomb structural bodies, however, have been associated with the following problems.
Specifically, when the partition walls of a conventional honeycomb structural body are narrowed to a thickness of about 100 .mu.m, an inconvenience results as the edges of the honeycomb structural body, i.e. the ends of the partition walls are abraded and damaged by the flow of exhaust gas. It is this narrowing of the partition walls beyond the conventional thickness which is believed to cause the lower partition wall strength and lower durability with respect to exhaust gas flow than is common.
As a strategy for fortifying partition walls when they are narrowed, the overall porosity of the partition walls has been lowered for greater density. However, while this increased density produces a strength-enhancing effect, it has led to such inconveniences as a higher heat capacity due to increased weight of the partition walls or poorer catalyst carrier properties.
In light of these problems of the prior art it is an object of the present invention to provide a honeycomb structural body with a lower-than-conventional heat capacity and excellent durability.